Feeding & growth

  This section on feeding & growth is divided into a part on larvae and a part on adults. A separate section deals with UPTAKE OF DISSOLVED & PARTICULATE ORGANICS.
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Research study 1

photograph of a sea cucumber Parastichopus californicusLaboratory culture of larvae of several species of echinoderms at Friday Harbor Laboratories, Washington, including sea cucumbers Parastichopus californicus, indicate a common pattern of suspension feeding.  The studies involve videotaping larvae as they capture 20µm diameter plastic spheres, while simultaneously recording elapsed time and later measuring lengths of ciliated bands, arms, and other features.  The drawing shows a drawing of a sea cucumber larva showing ciliary tracts used in food captureParastichopus auricularia larva of 1.2mm in length capturing a single plastic microsphere over a time span of 2.7sec. Note that the sphere is first captured on one of the ciliary bands to the right of the mouth and then a second time on a band just posterior to the mouth.  The particle then is moved toward the larval midline and into the mouth.  Interestingly, few particles, even these plastic ones, are lost after capture.  The author records only 29 incidences of loss out of 443 captures (6%).  Hart 1991 Biol Bull 180: 12; see Paltzat et al. 2008 Aquaculture 275: 124 for an account of joint culture of sea cucumbers P. californicus with Pacific oysters Crassostrea gigas.

NOTE the ciliated band of the larva is shown by the dark lines

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Research study 1
  histogram showing bimodal size distributin of sea cucumber species Pseudocnus curatus
Pseudocnus curatus
(Cucumaria curata) is a tiny species, rarely reaching sizes >20mm body length.  An early study of a population in Pacific Grove, California shows a bimodal size distribution.  Although the author does not discuss this, the data suggest a 2yr life span.  Felice 1950 The Wasmann J Biol 8: 39.
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Research study 2

drawings of tentacles of a sea cucumber Parastichopus californicus showing supporting spicule arrangementDepending upon species, adult sea cucumbers feed either by catching organic food particles suspended in the water column or by collecting detritus from the sea bottom.  Both methods involve the capture of food on tentacles arising from around the mouth.  In Parastichopus californicus, each of 5 major tentacles photograph of anterior end of a Parastichopus californicusbranch several times to make 5 mop-like structures with multiple adhesive pads or nodules.  When these are splayed against the substratum, food matter adheres, primarily through attachment to sticky mucus secreted by the skin, and secondarily through physical entrapment among the tentacle nodules.  The tubular rod-shapes of the tentacle nodules are maintained by calcareous inclusions, the dermal spicules (ossicles). The tentacles are periodically inserted into the pharynx where they are wiped clean against the pharyngeal wall.  Cameron & Fankboner 1984 J Exp Mar Biol Ecol 81: 193.

Anterior end of Parastichopus californicus with tentacles
withdrawn and mouth facing away from the viewer 1X

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Research study 3

photograph of anus and rectum of a sea cucumber Parastichopus californicusParastichopus californicus
feeds as it crawls slowly along.  Distance traveled is about 4m per day in photograph of two sea cucumbers Parastichopus californicus with their fecessummer.  daSilva et al. 1986 Mar Behav Physiol 12: 133.

Anus and rectum of P. californicus. The rectum doubles as a gas-exchange organ.
It is heavily muscled and rhythmic volume changes, combined with opening and
closing the anus, move water in and
out of large respiratory trees that
originate on the rectum's inner surface 2X

Parastichopus californicus
with characteristic ropey feces. The anus of one
individual is partly open. Fecal production in Parastichopus is continuous 0.7X

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Research study 4

scanning e-microscopical photograph of contracted tentacles of a sea cucumber Psolus chitonoidesPsolus chitonoides is a suspension-feeder, and the mechanism of particle collection is similar to that drawing of a sea cucumber Psolus chitonoidesdescribed in Research Study 2 for Parastichopus. Psolus catches organic particles in sticky mucus secreted by papillae on its tentacles or physically ensnares them in the papillae.  At rest, the papillae are withdrawn fully or partially (as shown on the Right); when feeding, they are extended as fine branchlets to expose more surface area (see photo in Research Study 5 below).  The tentacles are periodically inserted into the pharynx and cleaned of their load of particles.  Inorganic matter eaten along with organic material is passed through the gut to emerge with the feces from the anus.  Fankboner 1978 J Exp Mar Biol Ecol 31: 11.

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Research study 5
  With the exception of Parastichopus spp., most shallow-water west-coast holothuroids collect their food by suspension-feeding and by slurping the food off the tentacles. The tentacles are hollow and represent extensions of the main body coelom. They are expanded by forcing coelomic fluid hydraulically into them through contraction of body-wall musculature. Tentacles are inserted into the pharynx generally in alternate order, for example, 1-3-5-7-9-2-4-6-8-10-1. Here are some examples of sea cucumbers feeding:
photograph of sea cucumber Psolus chitonoides feeding
Psolus chitonoides in the process of pulling a tentacle out of its pharynx 0.5X
photograph of sea cucumber Cucumaria miniata feeding
One of the 10 tentacles of this Cucumaria miniata is inserted into the pharynx 1.2X
photograph of sea cucumber Cucumaria piperata feeding
Cucumaria piperata removing food from its tentacle 1X
photograph of sea cucumber Eupentacta quinquesemita feeding
This photo of Eupentacta quinquesemita shows the hollowness of its tentacles 2X
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Research study 6

graph showing growth of sea cucumber Cucumaria pseudocurata over a yearBlack sea cucumbers  Cucumaria pseudocurata in Sonoma County, California grow to adult size within a year of hatching.  This is a brooding species and, although documentation is needed, dispersal may be mainly by water movement. Aggregations on intertidal rock-wall habitats can be quite dense, a feature that may minimise desiccation during low-tide periods.

Survival after the first year of life is negatively correlated with density, at least on wall habitats (see graph on Right).  However, the author notes that individuals that go missing may not necessarily die.  Some may re-attach in another habitat, and this gives rise to the idea that water movements may be involved in dispersal.  Adults live to about 5yr of age.  Rutherford 1973 Mar Biol 22: 167.

NOTE  this species also lives amongst sea mussels and survival likely varies between habitats

NOTE survival is monitored in 16 cm2 quadrats located at +0.3m tide level

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Research study 7

A researcher at Catalina Marine Biological Laboratory, California provides data on ingestion and uptake of organic matter from sediment foods for the sea cucumber Parastichopus parvimensis. Rather than the sticky-pad method used by the closely related P. californicus (see Research Study 2 above) sediment uptake in P. parvimensis is described as solely involving hydrostatic pressure. Each of the 20 tentacles surrounding the mouth consists of a central stalk from which emanate many short horizontal branches each terminating in a cluster of small nodules.  As the photograph of tentacle end of a sea cucumber Parastichopus parvimensistentacle expands by increase in its internal hydrostatic pressure, sediment particles are trapped within the internodular spaces.  After insertion into the mouth the pressure decreases and the food particles are released.  A comparison of 2 populations show that individuals inhabiting granular sediments in coves ingest 8 times more organic matter than ones feeding on sediments coating the surfaces of rock rubble.  Although these latter are several-fold more numerous than the cove-bottom population, they are 27% smaller in size.  Feeding in all individuals ceases during Oct-Nov owing to annual evisceration events that affect 60% of all individuals.  There appears to be no size-selectivity when feeding, and sediments ranging from fine sand with silt/clay components are eaten the same as sediments comprised of coarse algal fragments.  Yingst 1982 Estuarine, Coastal Shelf Sci 14: 119. Photograph courtesy Udo Savalli, University of Arizona.

NOTE  although the author witnesses actual evisceration in some individuals, is it possible that, as in the closely related P. californicus, there may be visceral atrophy involved? (see Research Study 10 below)

Feeding tentacles and tentacular pads of a
sea cucumber Parastichopus parvimensis 3X

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Research study 8

The sea cucumber Leptosynapta clarki lives on intertidal mudflats along the Pacific coast from the islands of Haida Gwai, British Columbia to central California.  Studies at the Bamfield Marine Sciences Centre, British Columbia show that juveniles of 1-2mm in length are released from the brooding female parent via ruptures in the body wall in springtime, after which they immediately burrow into the sediment.  By August of the same year they reach a size of about 16mm and, by the commencement of reproductive period in November, are about 35mm in length and are reproductively active as males.  By 1yr of age they have reached a mean size of about 20mm.  Sewell 1994 Mar Ecol Progr Ser 114: 149.

NOTE  Leptosynapta clarki is a protandrous hermaphrodite

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Research study 9

histogram comparing distances moved in 24h by sea cucumbers Parastichopus californicusInvestigation of field growth in sea cucumbers, as in other animals, may require that individuals be tagged to identify them over time. To this end, researchers at the National Marine Fisheries Service, Alaska monitor retention rates of 6 types of tags1 by sea cucumbers Parastichopus californicus2 and assess post-tagging/handling effects on locomotory behaviour.  In laboratory trials, the single T-bar tag is found to have highest retention rate: 70% after 16wk and 40% after 32wk.  In field trials within naturally delimited plots, individuals tagged twice with modified T-bar FD-94 tags and ones “handled but not tagged3” move significantly further than “non-tagged” controls over 24h (see histogram).  On the strength of their results, the authors recommend that researchers minimise handling and wait at least 24h after tagging before using the tagged individuals in studies of behaviour.  The reader still wonders, though, whether it is the effect of  the tagging procedure, general handling, or the presence of the tag itself (T-bar tags apparently produce sores and lesions that may not be visible for several weeks) that leads to the increased locomotory activity.  The treatments are not clearly separated in the study.  These might repay further investigation, as would continued monitoring past the arbitrary 24h period set by the researchers.  Is it possible that the continued waggling stimulation of a T-bar tag in the epithelium or prolonged infection could lead to longer-term stimulation?  Cieciel et al. 2009 NA J Fisheries Management 29: 288.

NOTE1  these include Floy banner FTSL-73, cinch FT-4C, fingerling FTF-69, garment, single T-bar FD-94, and coded wire tags

NOTE2  the species supports small fisheries in all west-coast regions save for Oregon.  The flesh is used in different forms (pickled, dried, powdered) as a garnish in many dishes, and in stir-fry and soup preparations in many Asian countries

NOTE3  the researchers note that in order to monitor the “handled” and “control” groups in the field plots that would otherwise be visually inseparable, individuals that had actually been tagged one month previously, and presumably with the tags still retained, are used instead of individuals previously untreated.  The reader should bear this in mind when considering the results

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Research study 10

graph showing seasonal change in live mass in field cagesphotograph of juvenile sea cucumber Parastichopus californicusA study at the Pacific Biological Station, British Columbia provides data on growth of juvenile sea cucumbers Parastichopus californicus1.  The data are uniquely derived from 20 individuals maintained in each of 3 cages (each 90 x 60cm, mesh covered) on shell-sand seabed at 15m depth over a 12mo period commencing September 2008.  In that time live mass2 increases about 160% on a diet of natural sediments.  Loss in live mass from late summer and through winter is thought by the authors to owe to decreasing temperatures and reduced sediment deposition, as well as to visceral atrophy3.  This is a seasonal phenomenon in P. californicus and involves absorption of all internal organs with later regeneration.  Hannah et al. 2012 North Am J Fish Managem 32: 167.

NOTE1  this species supports a commercial fishery in B.C. with an annual value of 2.6 million$Can from a harvest of 600 tonnes (in 2007; data based on “split” mass, that is, after removal of the guts)

NOTE2  variable water content in sea cucumbers makes live-mass estimates imprecise, so the authors present their data also as immersed whole mass (not included here)


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